1. Field of the Invention
The present invention relates to an optical recording medium such as an optical disk, etc., and more particularly to an optical recording medium suitable for high-efficiency recording and reproduction of information at a recording density below the optical resolution.
2. Related Background Art
For example, U.S. Pat. No. 5,153,873 discloses a typical example of the conventional technology for recording and/or reproducing information at a recording density below the optical resolution in an optical disk apparatus etc. In this technology, the recording and/or reproducing of information at a recording density below the optical resolution is realized by using a medium in a laminate structure in which a layer made of a nonlinear optical material is laid on a recording surface, and, further by, while irradiating said medium with a reproduction light spot, greatly changing an optical property, such as a transmittance or reflectivity, etc., of said layer only in a small region within the reproduction light spot, so as to reduce an effective spot diameter effective for reproduction. Also, the U.S. Pat. No. 5,153,873, for example column 6, lines 39-47, lists inorganic materials such as gallium arsenide, indium arsenide, and indium antimony as specific examples of the nonlinear optical material.
There are, however, the following problems in forming a film where such inorganics are used as the nonlinear optical material.
The method of vacuum deposition such as vapor deposition or sputtering is used for forming the inorganic film, but this method is poor in productivity and it is hard to obtain a thick film. This excludes materials which cannot show a sufficient change in the optical property without giving a considerable film thickness, which narrows the range of selection of materials.